This set of models shows the effect of damping provided by rubber bands in free vibration, which can be heard by ears.

(a) (b)

Fig. 17-3: Effect of damping on sound transmission

The sound heard from the free vibrations of a taut string, such as a violin string, links two different physical phenomena, sound transmission and the string vibrations, which both can be described using the same differential equation of motion. Thus hearing sound can be related to observing free vibrations, in this case those of a taut string.

Fig. 17-3 shows two identical steel bars, one is a bare bar and the other has rubber bands wrapped around it. The effect of the damping added by the rubber can be demonstrated as follows:

Suspend the bare bar and give it a knock at its lower end using the other metal bar as shown in Fig. 17-3a. A sound will be generated from the bar for several seconds as it reverberates.

Suspend the wrapped bar and give it a similar knock on the exposed metal part (Fig. 17-3b). This time only a brief dull sound is heard as the rubber wrapping dissipates much of the energy of the vibration.